A roof window assembly is composed of a window component, a main frame component and, optionally, an integrated flashing component. The window component may be used independently and without modifications for a roof window installation employing a curb-frame. The window component features a novel design with an glazing element fitted in a profiled sheet metal frame, which can be made from a single continuous sheet metal profile bent into a polygonal frame shape with corner junctions. In both fixed and ventilating versions of the roof window assembly identical connecting members into open mutual engagement at the top side of the window and main frame components provides for easy mounting and dismounting of the window component with respect to the main frame component. The flashing component comprises a rigid flashing frame arrangeable against outer side faces of the main frame component and foldable resilient side flashing sheets, which can be folded to allow packing of the flashing component together with the window and main frame components into a single unit comprising all components needed for installation of the roof window assembly.